SUMMARY: Six new side-chain liquid crystalline polysiloxanes with thioether type spacers bearing cyanobiphenyl or nitrobiphenyl moieties at the termini were prepared by hydrosilylation of a-thioether groups containing olefins in the presence of hexachloroplatinic acid. The rates of grafting are higher than 90% on condition that the a-olefin does not contain sulfur atoms in allylic position. All the obtained polysiloxanes present the SmA d mesophase. Sulfur permits one to obtain long spacers without resulting in of crystallization.

SUMMARY: Two chiral liquid-crystalline polymers with polysiloxane main chains, thioether type spacers, and biphenyl derivatives bearing one or two chiral atoms as mesogens were prepared by polyhydrosilylation of polymethylhydrogenosiloxane with a-thioolefins carrying biphenyl-based mesogens in the presence of hexachloroplatinic acid. The polymers exhibit two mesophases as a function of temperature. The nature of the first mesophase depends upon the nature of the chiral substituent of the biphenyl, but the second one is always of the SmC * type and covers a large range of temperature.

SUMMARY: A series of nine liquid crystalline polysiloxanes was studied by means of dielectric spectroscopy. These polymers contain thioether spacers with different length, a diphenyl unit as mesogenic group and end-groups with cyano, nitro or one or two chiral centers. Another liquid crystalline polymer, without sulfur atom in the spacer, was studied in the same conditions. The dynamics of these polymers shows four molecular relaxation (a, ) processes, and a collective (Goldstone mode) relaxation process for chiral polymers. The a relaxation temperature decreases with increasing spacer length due to the sulfur atom. On the other hand, the thioether spacer prevents cristallinity.